US2377474A - Measuring instrument - Google Patents

Description

June 5, 1945. A. F. ALLWEIN MEASURING INSTRUMENT Filed March 25, 1943 4 Sheets-Sheet 1 INVENTOR. ALOYSIUS F ALLWEI N A. F. ALLWEIN MEASURING INS 'I'RUMENT June 5 1945.

Filed March 25, 1943 FIG. 3

4 Sheets-Sheet 2 INVENTOA-Rfl ALOYSIUYS F. murmur:

June 5, 1945. A. F. ALLWEIN MEASURING INSTRUMENT Filed March 25, 1943 4 Sheets-Sheet 3 FIG.6

INVENTOR.

ALOYSIUS F. ALLWElN June 5, 1945. A, F. ALLWEIN MEASURING INSTRUMENT 4 Sheets-Sheet 4 IN VEN TOR.

ALQYSIUS F. ALLWEIN ATTORNEY.

Patented June 5, 1945 a. If 2 311,414"

Aloysius Allweindhiladelphm, :Pa.,= A I vThe Brown Instrnment Company,.l'hiladelphia,- e l'a acorporation of Pennsylvania The present invention relates to measuring instruments, and particularly to measuring instruments oi-the" multiple seli balancing potentiometer type and to means for automatically recalibrating or standardizing them aten m i *tervals.

As is well known the voltage sup l g potentiometer instruments is-.derivedj from a' dry cell. While such a'source is substantially ton- -"st'ant, there is, over a period'og timega decrease in'the voltage produced. Such a decrease will not prevent the instrument fronibalancinglitself, but

cause'the balance point-to be inaccurate.

Periodicallm 'therefore, a resistance in series with the dry cellis adjusted to bring the potential drop across the slide-wire to some standard value in order to maintain the accuracy of the instrument. It is'an object of this invention to provide a simplified means for adjusting-the standardizing resistance of a potentiometer'circuit. It is a otFigureB v a Figure a'isaviewshowing the'lost motion con- 1 Figure 5jis aview taken on line 58 of Figure 3, Figure 6' is a. back view of .a. portion of the 7 instrument the standardizing resista v .Y

'l is apartialjyiew taken from the left nection in fthes'tands.rdizing rheostat,

Figure 9 is ti -sac: viewoi a modified type of s n a q i sm an and 'Figurelo is a view partly in section taken from {the right of Figure ,9.

InFi'gure l-there'is shown atypical potentiometer circuit in which there is a slide-wire f that has a 'potential impressed across it by a battery 2 to produce a predetermined voltage drop;

the battery preferably being in the form of a dry cell. Connected in'circuit with the battery is a variablefresistance I that 'is used to maintain further object of the invention to have the standardizing resistance of a potentiometer circuit ad- .iusted by means of the same powerdevice which serves to drive the marking element across the chart, and which driving mechanism is operated whenever an unbalanced condition of the'potentiometer circuit occurs. It is a further object of the invention to provide potentiometer standardizing means which is automatically operated at periodic intervals. to standardize the potentiometer circuit. It is a further object of the invention to prevent a record of the condition being measured from being made during the time that a standardizing operation is taking place.

The various features or novelty which characterize this invention are pointed out with particularity in the claims annexed to and iorming a part of this specification. For a better understanding-oi the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawings and descriptive matter in which is illustrated and described a preferred embodiment of the invention. In the drawings: I

Figure 1 is a wiring diagram of a multiple potentiometer circuit, e

. Figure 2 is a top view partly in section of the drive mechanism for the print wheel of the po- 'tentiometer,

Figure 3 is a side view showing the print w-heel actuating mechanism and' the standardizing mechanism,

Figure 4 is a view showing the timing means for the standardizing mechanism,

' the slidewire i as determined by the position 0! constantthe potential drop in the circuit as the battery diminishes in power in order to maintain the system in" calibration. Thevoltage from a thermocouple l 'isj impressed across a portion or a contact 5 between the slidewire and a parallel collector bar 6. As the thermocouple temperaturechangeathej, potentiometer circuit becomes unbalanced and this in turn is detected by a vibrator and amplifier unit 1 to energize a motor 8 to shift the conta'ctfalong the slide-wire in the proper direction and amount in order to rebalance the potentiometer circuit. The details of the vibrator and amplifier are disclosed in the co-pending application 01 Walter P. Wills, Serial No; 421,173,'and which was, filed on December 1, 1941, and they are characterized by the ability to continuously energize the motor 8 for rotation in the proper direction whenever the potentiometer circuit is unbalanced.

The thermocouple is normally connected in the circuit by means or a switch 8 which consists of a movable contact ii that is directly connected to the amplifier and a stationary contact I! that is connected to the thermocouple. This switch is also provide'dwith stationary contact I! that is connected to the potentiometer network, and stationary contact ii, that is used to insert a shunt couples subjected thereto. To this end. there is In the operation of a potentiometer network of the type disclosed above, upon the occurrence of a change in temperature 01' a thermocouple 4 the potentiometer circuit will be unbalanced to produce a current flow in one direction or the 5 other through the vibrator which is included along with the amplifier anddesignated as I. The V1- brator and amplifier-will detect this unbalance,

. its direction and-amount, and correspondingly energize the motor 8 for rotation in the proper direction. This motor is mechanically connected;

in a manner to be described, with the contact 5 so that the latter is shifted alongthe slide-wire i and collector 6 to a positionin-which the po-"--" tentiometer circuit is again .rebalancedand no current flows through the unit 1.

Due to the fact that the strengthot the battery r g to disconnect the thermocouple ,from the circuit and toinsert the standard cell'll across"a portion thereof and to simultaneously insert the shunt it around the unit]. I! the circuit needs recalibration a current now will be produced "through the unit fl in a manner similar to that produced bythe' thermocouple 4, producing. an

"energization oi the motor I to rotate this motor in a direction and an amount proportional to the potentiometer unbalance at that time. This rotation or the motor is used to adjust the amount oi the resistance 3 which is inserted in the circuit. In some cases the potentiometer instrument is designed to measure sequentially the value or a number or temperautres as measured-by thermoshown in Figure 1 a series or thermocouples is, It and 20 in addtion to the thermocouple 4 which may be connected in the potentiometer circuit one after another in any'conventional manner by means 01a suitable thermocouple switch. The invention in this case is particularly directed to the potentiometer standardizing mechanism per se and this mechanism in combination with the remainder of the potentiometer structure. The potentiometer mechanism shown herein is 01 the type disclosed in detail and claimed in the a r plication of J. A. Caldwell, Serial No. 447,863, which was filed on June 20, 1942, and reference is accordingly made to that case for details of the otentiometer structure which are not shown herein and which form no part of the present invention.

Referring to Figures 2, 3 and 6, there is shown broken away an instrument casing 2| in which the entire potentiometer mechanism is located. This casing is provided with a door 22 that is hinged at 23 and may be swung out of the way to give access to the structure to be presently described. A casting 24 upon which the potentiometer structure is mounted is hinged at 2! in the casing, ahd may be swung from the position shown out oi the casing when the door22 is opened, to give access to the structure. carried thereby for adjustment and repair. The casting 24 is provided with a compartment" on its left side, and with side plates 21 and 28 that are joined by a connecting wall 29. The support 3| for the slidewire i is mounted between the side plates 21 and 28, and carries this slidewire along with the collecting bar 8 on the lower side thereof as is shown best in Figure 3. Beneath the slide- 7 v ionv 42 ,extendsito;. the, rear. of 'wall whem it the motor 8 Irony driving the..-print-,wheel carriage and}. thecontact carried therebywbeyond wire and suitably mounted for sliding movement across the instrument is a print wheel. carriage 32 which has attached to and insulated from its upper surface the contact 5 so that this contact may engage the slide-wire and the collector bar as the carriage 32 is moved transversely of the instrument. ,Theprintifwheelrr'i 'agfe is gdriven by means of a"'cable*33"which sits'ends attached to the carriage, and which passes over pulleys 34, I5, 38 and 31, the latter of which is biased in a counterclockwisesdirection in order to take up any slack in the cable. The cable 33 is driven by a large puIIey'SB 'asshown in Figure 6. This pulley is attached to a gear 39 that is mounted for rotationon-theshait 4|, and the pulley and'the gear- ;are driven together by means of a pinion 42 that is on the shaft of motor 8. This motor is moun'ted beneath the print wheel carriage and on the trout portion or thewall 28, while the pinmeshes with ,the gear. 39 andthe'stmcture carried thereby. ,-The, gear I 39 is providedwith a i 4 4 M. sst 9 .w nit e ages one side or the other of the pinion 42, to prevent ',the ends. I the slide-wi in either direction.

Th'e' operation or ,the. instrument ,is such that .occursthe motorliwill b e,rotated in the-proper when an unbalance .in the.,potentl0meter circuit direction wanvage 'r 38 and pulley J8 sqthat the cable wrapped around the pulley will shift theprint wheel carriage transversely between the 35 side plates oi the. instrument casting. As the print wheel carriage moves, the contact I carried thereby will be moved along the slide-wire l untii the potentiometercircuit isrebalanced, at which time the motor willstop.

The print ,wheel carriage has pivoted iin it a support .44 uponwhich is mounted a print wheel 1 45; This support amovedfin a manner tobring the print wheel into and out of engagement with correspondinfto the, value oi the temperature being measured at that time by, instrument.

The jchart is 'fed from a supply roll that is not shown over a chart drum 41, and'is supplied to a chart take-up roll that is not shown. The

'chart drum '41 lis/driven at a suitable speed by means of a train of'gears that is in turn 'drivenirom a pinion 49 which isconnectedflto the shaft of a suitableconstant speed drive motor. In the operation of the instrument, the motor 8 serves, through connections previously described, to shift the print wheel carriage transversely of the instrument to a position above the chart corresponding to the temperature which is then being measured. Thereafter the support 44 is moved in the print wheel carriage to bring the print wheel into engagement with the chart and is moved out of, engagement with the chart. Simultaneously, the instrument is connected to another one of the thermocouples so that the rebalancing operation may berep'eated.

The movement of the support 44 is accomplished by means or .a compound lever II, 82 that is oscillated around. ashaft 53. As the compound lever oscillates the portion 52 moves a channel member 54 thatis-attached thereto: and whichextends transversely oi theinstrument. This channel member receives a roller 55 that is attached to the rear end of the support 44. Therefore, as the channel member is moved up and down the print wheel 45 will be moved into and out of engagement with the chart. The lever is oscillated by means ofe se e be tween a slot 56 formed therein and a roller 51 on the end of a crank 58 that serves to rotate a shaft 59 to which it is attached. 'The crank is rotated clockwise by means of engagement between a pin 6| on its short arm and a cut out portion 62 formed on one of the pawls 63 which are pivoted on*a cam 68 that rotates around the shaft 68. In the position shown the pawls are in such a position that their cutout portions 62 are at a radial distance from the shaft 58 suflicient so that they can be moved past the pin 6! without engagin the same, but when any one of the pawls is rotated clockwise around its pivot from the position shown to the dotted line position shown with one ofthe pawls, the cut-out portion 62 will be moved radiallyjinward to a position in which it will engage the pin 6| and rotatethe crank 58 therewith. The pawls are' moved from the position shown in solid lines into the dotted line position by means of engagement between the end 64 of a detector member 68 and a central raised portion 86 formed on the leading end of each pawl. from their dotted line position to the full line position by means of engagement between the end 64 and one or the other of raised portions 61 which are formed at the sides on'thetrailing end of each pawl. The detector member. 65 is frictionally mounted for movement with the pulley 34 so that as this pulley rotates when the instrument is unbalanced and the print wheel carriage is being moved, the detector will be moved to one side or the other of the position shown in Figure 2. As shown, the cam 68 is a three lobe cam thatis rotated around. the shaft 59 in a clockwise direction by means of suitable gearing that is driven from the constantly rotating pinion 49. The pawls are held in their solid line or their dotted line positions by means of springs 68 which are attached to the cam68 and engage the rear end of the pawls.

The cam 68 is continually rotated to bring its raised portions into the V-shaped opening formed in the detector member 65 to periodically bring this member to the position shown in Figure 2. If the instrument is unbalanced, and the pen carriage is being moved, passage or the cable 33 over pulley 34 will move the detector 65 to one side or the other of the midposition shown immediately after it has been straightened out by the cam 68. Each time th end 64 of the detector member is moved out of its central position it will be in the path of one of the portions '61 of the pawls to move the next pawl passing it to the full line position shown. If, however, the instrument has reached a balanced condition, the detector 65 will remain in its mid-position where it is moved by the cam 68 and the end 64 will then be in the path of the raised portion 68 of the next pawl moving past it. That pawl will then be moved to its dotted line position to bring the cutout portion 62 into the path of pin 6! and will therefore rotate crank'58. As the crank rotates roller 51 will move the compound lever ii, 52 first slightly clockwise to bring the print wheel into engagement with the chart, then counterclockwise, and then back to the position shown. During the movement of the lever, the

The pawls are moved back Figure 2 sovthat its end 84 will engage one of the projections 61 on the pawl which has been driving crank 68, and move this pawl to the full line position so that the crank will remain in the position of Figure 3 until such time as the instrument again reaches balance, and th above operation can be repeated.

The standardizing resistance which is shown diagrammatically in-Figure 1 is shown in detail in Figure 7 as consisting one. vernler rheostat which is made of a flneresistance II and a coarse resistance 12 which resistances are rotatably .mounted on a shaft 18 that-extends rearwardly from the wall :28 of the mechanism supporting casting 24. The arrangement is, that the fine resistance is adjusted" directly and the coarse resistance is rotatedby the fine resistance by means of a pin 14 which is attached to the fine resistance II and extends rearwardly therefrom through a slot 15 that is formed in the resistance 12. The resistances are engaged by a split contact 16, which contact serves the purpose of connecting these resistances in the potentiometer circuit, and also by its frictional engagement with the resistance discsserves to prevent accidental rotation of the latter. 4 i

The resistances are adjusted relative to the contact I6 by means of a clutch which comprises a driven clutch disc 11 that is formed as a part of the resistance H, and a driving clutch disc 78 which is also rotatably mounted on the shaft 13, and is attached to agear 18. The gear 19 meshes with pinion 42 driven by the motor 8 so that as this motor rotatesthe gear and the drivin disc 18 also rotate andat predetermined times, when the clutch discs .11 and 18 are in engagement with each other, serves to adjust the resistance 8. Driving disc 18 is moved into or out of engagement with driven disc 11 by means of a lever 8| that'is attached to a shaft 82. The upper end of .this lever has a roller 83 which enases the left face of the clutch disc to move this disc to the right into engagement with the disc 11, or the right face of gear 19 to separate the discs. During the movement of the disc 18, gear 19 will slide along the pinion 42, the latter being wide enough to permit this to take place. The shaft .82 also has attached to it a second lever 84; the two levers and shaft being biased in a clockwise, or clutch closing direction by means of a spring 85. The lever 84 also has an extension 86 projecting rearwardly from it which serves, by means of a pin 81, to throw the standardizing switch 9 from the position shown in Figure 1 to a position to bring contact H into engagement with contacts l3 and I4 whenever the clutch is closed. The switch 9 is shown in Figure 7 as being of a leaf type, and is mounted on a support 88 which is adapted to be fastened as shown at 89, to the wall, of the casting.

Normally speaking, during the operation of the instrument, the standardizing mechanism parts are in the position shown in Figure 7, and are held in that position by means of engagement between a roller HI and a cut-out portion 90 on the upper end of lever 84. The roller 9| is mounted on a crank 82 that is attached to a shaft 93. This shaft is periodically rotated, in a'manner presently to be described, so that the instrument may standardize itself. It is noted that the contacts 16 are supported on a member 94 that is attached to the outboard end of shaft '13. The support 94 also has a pin 95 projecting inwardly from-it that serves as a stop to limit rotation of the resistance members H and 12. when the resistance members have rotated to one or the other of their limits pin 10 will'engage pin" to stop their rotation.

The shaft is periodicallyrotated to permit a standardizing operation to take place by means of a crank which is located in the right end of th shalt, as shown in Figure 8, and in the compartment 28 as shown in Figure 3. The crank is driven bya pawl arrangement similar to that used to rotate the crank 58 which controls the printing operation. To this end, the crank 96 is provided with a pin 91that'is adapted to be engaged by a pawl 98.;which is pivotally mounted on a gear 99. Thispawl is provided with a cutout driving portion 82 and raised portions 88 and 51, exactly like those portions which are formed on Dawls 53. The ear 99 is driven in a counterclockwise direction in Figure 3 by means of suitable gearing between that gear and the constantly driven drivepinion 09. The pawl 98 is normally held in the position shown in Figure 3, in which position it will not engage the pin 91 todrive the crank. The pawl may be moved to a position to bring cut-out portion 92 radially inwardly so that it will engage the pin 91 and rotate the crank by means of the tip I02 of a lever I03 that is pivoted on a shaft I04. When the lever I03 moves to the dotted line position of Figure 5 its tip I02 will be inthe path of projection 98, and upon engagement therewith will move the pawl 99 into driving engagement with pin 91, but when the lever is in the full line position of Figure 5, the pawl I02 will lie in the path of the outer one. of the projections 51 to keep the pawl normally in its non-driving position. If the lever I03-has been moved to its dotted line position and the pawl 98 moved to the position in which it engages pin 91, an arm I09 formed on the lever will be in the path of a bent out portion I08 on the opposite end of crank 99. As the portion I05 passes arm I08 it'will move the lever I 09 counter-clockwise in Figure '5 so that the tip I02 thereof will be in the path of projection 01 of the pawl 90' to move the pawl out of its driving position.

The lever I03 is normally held in the full line position of Figure 5 by means of eng ement between a portion I 01 thereof and a stop lever III that is pivoted at II2. When the stop lever III is moved in a clockwise direction in Figure 4, or downwardly in Figure 5, the lever I03 can move clockwise in Figure 5 or to the left in Figure 4 so that. its portion I01 will engage a surface I09 on to lever II I, thus permitting the lever I 09 to move into its dotted line position. The lever I09 is normally biased in a clockwise direction in Figure 5 by means of a spring II! so that the lever will tend to engage one of the portions I08 or I09. The stop lever III is normally blased in a counter-clockwise direction in Figure 4 by means of a spring Ill to keep this lever in engagement with the portion I01.

Lever III is periodically moved clockwise in Figure 4 to permit a standardizing operation to take place by means of engagement between the projection IIO of that lever and a pawl III! that is pivoted at II 8 on a ratchet II1. The pawl is biased by means of a spring IIO so that it normally engaged a pin II9 which also is attached to the ratchet H1. The ratchet is rotated in a counter-clockwise direction in Figure 4, and a clockwise direction in Figure 3 by means of a pawl I2I that is pivoted to a rocking lever I22. This latter is pivoted at I28 and is moved around its pivot against the action of a spring I 20 by scribed, to take place.

in standardizing condition until such time as the means of a pin I20 that projects from the gear 99. Th arrangement is such that the ratchet and the gear are both freely rotatable onthe shaft 88 with the driving lever I22 located between the two. The ratchet is driven in a direction opposite to that of the gear 99 so that the gear will not have any tendency to pull the ratchet ahead faster than it would normally be driven. Thelever I 22 is biased by its sprin I20 into engagement with astop pin I25. Adjusting this pin with respect to the pivot I23 willdetermine the amount of throw given to the lever I22 on each revolution of the gear 99. It is noted that holding pawl I26 engages the ratchet ill to prevent retrograde movement of the latter. A pin 121 which lies in the path of the pawl III extends outwardly from the frame 21 and into the path of this pawl for a purpose to be later described. It is also noted that the holding lever III may be moved by a rod I28 which projects forwardly through the front of the frame,- as well asby the pawl I I5.

In theoperatlon of the standardizing mechanism the gear 99 is rotated at a constant speed, and on each rotation thereof the pin I20 acting through lever I22 and pawl I2I serves to rotate the ratchet I I1 for a predetermined distance. As the ratchet rotates, it will carry pawl H5 in a counter-clockwise direction in Figure 4 until this pawl engages the stationary pin I21. Thereafter, continued rotation of the ratchet I I1 while the outer end of pawl I I5 is held still, will cause the spring II8 to be tensioned. Eventually the ratchet will reach a positionin which the end of the'pawl will run on! of the pin H1, and under the force 0! spring IIII this pawl will be moved downwardly into engagement with extension 0- of the holding lever III. The blow that is given to this extension '0 by the pawl is sufilcient to move the lever III against the force of its spring II to'move projection I08 out of engagement with the extension I 01 of the lever I03. Lever I03 may therefore turn clockwise in Figure 5 to its dotted line position with the extension I01 engaging surface I09. At this time the tip I02 of the lever is in a position to engage the pro- Jection 88 of the pawl 98. The pawl will accordingly'be moved into its driving position to rotate the crank 98. As the crank is rotated, roller ii on the opposite end of shaft 93 will be moved out of the low portion on lever 84 to permit the standardizing operation, as previously de- The instrument will be crank 96 has made one complete rotation. When this occurs the portion I00 of the crank 96 will engage portion I08 of lever I03 to move the lever from its dotted line to its full line position of Figure 5, and thereby bring portion I01 to the left of the projection I08 in Figure 5. Spring I will thereupon move the stop lever III to a position in which I01 may engage I08. The parts will remain in this position until such time as the pawl I I5 again engages the extension IIO to repeat the standardizing operation. The speed of rotation of gear 99 is such that the instrument will have sufficient time to standardize itself during one rotation of the gear and crank 92. The standardizing operation may also be performed manually by the operator by merely pushing the right end of rod I28 in Figure 3. This operation also moves the stop lever III clockwise in the Figure 4 so that lever I03 can turn from its full line to its dotted line position in Figure 5. Upon the next rotation of the gear 39 the instrument will Standardize itself in the manner above described.

It is necessary to prevent a printing operation from taking place during the time that the instrument is being standardized in order to prevent an incorrect recording of the value of one of the conditions from being made. As far as the recording portion of the instrument is concerned, a record will be made each time the instrument comes to balance, but if the instrument has been standardized, and a record is made, the record will merely be of the standardizing, rather than the temperature of the thermocouple to which it is then connected. To prevent this from occurring, the printing mechanism is not operated during the time that standardizing takes place. This is accomplished by a means which holds the detecting member 85 in its outof-balanee position during such time as the standardizing switch is thrown and the standardizing clutch is closed. To this end, the shaft 93 is provided with a cam I29 having a raised portion I3I against which the tip I32 of a lever I33 normally bears. This lever is pivoted at I34 and biased in a clockwise direction in Figure 6 by a spring I38 so that its upper end will tend to move a pin I35 against the side of the detector member 55 to push this member out of its neutral position. The parts are in the position shown in Figure 8 when the instrument is being operated normally. When a standardizing operation takes place, however, rotation of the shaft 93 will move the raised portion I3I of cam I39 past the end I32 of lever I33. At this time, spring I33 will move the lever I33 so that its upper end will force pin I35 against the side of the detector member 65. As the cam 68 straightens the detector member out during its rotation, the cam lever I33 will merely be rocked around its pivot I34 against the tension of spring I38 by means of the action of pin I35. When the standardizing operation is completed, the cam I29 will have made one complete rotation to bring its high portion I3I back underneath the portion I32. Lever I33 is then held in a position in which it cannot act on the pin I35. The instrument can then operate in its usual manner.

In Figures 9 and 10,there is shown a modification of the clutch and switch operating mechanism which may be used in place of that which has been previously described. In this case, the

shaft I3 which supports the two rheostats II and I2 is rotatably mounted in a sub-frame I that is attached to the wall 29. The gear I9 which serves to adjust the standardizing resistance 3 is located between the frame I and the wall 29. This shaft I3 in addition to having the rheostat rotatably mounted on it, has a clutch disc I42 attached to its outer end. The clutch disc has built into it a spring I43 which bears at one end against the clutch disc and at the other end against an abutment I44 that is formed on the rheostat I i,the left face of which acts as the second clutch disc. In this fashion, the shaft I3, the clutch disc I42, and the gear I9 are resiliently pressed toward the left to keep the clutch open during normal operation of the instrument. The clutch is closed as the shaft I3 is moved to the right by means of a bent over portion I45 which engages the end of the shaft 13, and which forms part of a. lever I46 that is pivoted on a stud shaft I61. Also pivoted to this shaft is a second lever I49 that is resiliently held in a given position relbetween a pin I49 that projects from the lever I48 and bears against the edge of lever I49. The levers are held in their relative position by means of the action of a spring I II that acts on lever shaft I3 to the right. This moves clutch disc I42 against the face of resistance II to close the clutch. This same operation of lever I48 serves to operate switch 9 to disconnect the thermocouple from the potentiometer circuit and' to connect the standard cell in the circuit in its place. For this purpose, the lower end of lever I48 is provided with a bent over portion I54 through which a screw I55 is threaded. This screw bears against the long blade II of the standardizing switch 3. Normally speaking, the resiliency of the switch blade acting against the screw I55 maintains the lever in the position shown in which roller I52'bears against the cam I53. -The switch in this case is mounted on a portion I56 of a plate I51 that is attached by screws I 53 to the sub-frame I. As shown in the drawings, the plate is in solid lines in Figure 9. but is shown only in outline by dotted lines in Figure 10. The reason for the showing in Figure 10 is so that the plate will not hide a large number of parts that that figure is intended to disclose.

This embodiment of the invention is also provided with a stop to limit the rotation of the resistances II and I2. The stop consists of a pin I59 which projects rearwardly from the support I4I into the path of the pin I4. When the resistances have rotated to one or the other of their limits, pin 14 will engagepin I39 to stop their rotation.-.

The operation of this standardizing arrangement is'the same as that previously described.

When the ratchet III has rotated sufficiently it will cause the pawl 98 to drive crank 96. This rotates shaft 93, and the cam I53 carried thereby.

as the cam'rotates it will move the lever I43. I48 in a counter-clockwise direction to simultaneously close the clutch and throw the standardizing switch to a position in which the standard cell is connected in the potentiometer circuit Upon the completion of a single rotation of shaft 93 the standardizing operation will be completed and the parts return to the position shown.

At times it may be desirable to have some indication as to the condition of the battery 2 so that the operator may know when this battery is to be renewed. For this purpose an indicator is provided. which consists of a bell-crank lever IBI that is pivoted at I52 and normally biased in a counter-clockwise direction by a spring I53 to the position shown in Figure 9. As the battery 2 diminishes in strength, the resistance will be adjusted in a counter-clockwise direction in Figure 9 until such time as the pin I4 between the resistances engages the upper surface of the horizontalarm of lever I6I. Continued rotation of the rheostats will thereafter cause arm I BI to move in a clockwise direction. When the arrow on the vertical portion of this arm is in line with the pointer I64 that is formed on the sub-frame Hi, the operator will know that the battery should be renewed.

- tion is normally-intended to be automatic, it can be initiated manually at any time'by. the opera- ,tionof a button. Thereafter, the instrument will automatically -operate the standardizing mechanismiust asii it was operated by the timing device. 1

- Whilein accordance with the provisions of the.- I

statutes, I have illustrated and described the best form of my invention now known .to me,'it will be apparent to those skilled in the. art :that changes may be made in the form: or the appsratus zdisclosed without departing :Irom the spirit oi my invention as set iorthin theappended claims, and that in some cases certain features of my invention may sometimes be used .to advantagewithout acorresponding use of other features. I

Having now described ,my, invention. what I claim as new and-desire to secure by Letters Patent is: r

1. In a potentiometer instrument of the selfbalancing ype the combination of-meanscontinuously operating when the potentiometer is unbalanced to rebalance the same, standardizing means for said potentiometer driven from said continuously operating means, a clutch imposed between said last two .meansrmeans to periodica1ly '"operate.-. said clutch comprising a constantly rotating member, a drive part carried thereby movable from operative to inoperative positions, a member to be rotated by said drive part when the latter is in its operative position, ;a clutch controlling means connected to said member. and *means' to move periodically said drive -;part into it; operative posit on. 1-

2.,In a self-balancing type'potentiometer in strument the combination of means to stand ardize. the instrument comprising a-constantly rotating member,-a drive part movable from operative 'to inoperative positions carried by said member, a driven part operated by said drive part, meansmovable from a first position in which it isoperative to move said drive part to its oper-' ative position to a second position in which it is' operative to move. said drive part to its inoperative position, periodically operated mechanism to move said movable means to its first position, and means forming part ot-said driven part to move said movable means-to its second position.

- 3. In a self-balancing type potentiometer instrument, the combinationot means to-sta'ndardize the instrument comprising aclutch mechanism,-means to bias said-clutch to an open position, means .to close said clutch including a driven part, a driving part movable i'rom operative to inoperative position, periodically operated mech-' anism acting in one'position to movesaid driving part to operativeposition so that it may operate said driven part and acting in a second position to move said driving part to inoperative position, and means forming a portion of said driven part to move said periodically operating mechanism to its second position. i

4. In a seli-balancing potentiometer instrument, the combination of means to standardize said instrument including a clutch normally biased to an openposition, means to close said clutch including a rotatable driven part,'a rotatable driving part movablefrom an operative to an inoperative position, means acting in one position to periodically move said driving part to its operative position whereby it will operate said driven part to close said clutch and permit standardizing of the-instrument to take place and .acting in a second position to move said driving part to inoperative position-and means forming part of said driven part to move said periodically moving.v means to its second position upon the completion of one revolution of the driven part.

5. In a self-balancing yp potentiometer instrument having means to standardize the same including a clutch and a switch, means to simultaneously operate the clutch. and switch including a rotating member acting-upon a complete rotation of the same tocomplete a standardizing cycle, a crank having a-pin projecting therefrom. connecting means between said crank-and member, a rotatable drive pawl movable from a position-in which it will engage said pin to rotate said crank in a position inwhich it will-not enmember to control the movementot said driving part into engaging position, latch mechanism for said member, and means to operate said latch including a rotating part, a pawl carried thereby and movable through a path intercepted by said latch, resilient means to bias said pawl to a predetermined position with respect to said rotating part, holding-means tomove said pawl relative to said rotating part as the latter is moving where-' by said resilient means will be tensioned, continued rotation oi said rotating part moving said pawl away from said holding means, the tension builtup-ln said resilient means thereby to move said pawl against said latch with force enough to release the same.

7. In a self-balancing type potentiometer instrument comprising standardizing mechanism, the combination of means to operate said mechanism periodically comprising normally disengaged driving and driven parts, a member to produce engagement of said parts, latch mechanism to hold said member in inoperative position and means to release said latch mechanism comprising a moving part, a latch releasing device carried by said part and movable through a path intercepted by said latch, resilient means to bias said device to a given position relative to said part.

means to hold said device relative to said part to tension said resilient means then release said device, the force of said resilient means being suillcient to cause said device to act on said member and release said latch.

8. In a self-balancing potentiometer instrument including standardizing mechanism, the combination 01' means including a latch mechanism to control the serving operation of said standardmechanism, a rotating member, a-device carried on said member, resilient means to bias said device to a given position relative to said member, means to hold said device to tension said resilient means as said device moves through its path and then release said device whereby said resilient means will forceably move said device back to its given position relative to said member, said latch mechanism being located in the path of movement of said device as it moves to its given position to be actuated thereby.

9. In a sell-balancing type potentiometer having a standardizing mechanism including a clutch and a switch, means to positively operate said clutch and switch in opposite directions comprising a pivoted lever biased in one direction in which the clutch is closed, means to move said lever in the opposite direction and hold it in a position in which the clutch is open, a rotatable part to operate said moving means, a driving part movable from a position in which it will operate said rotatable part to a position in which it will not operate said rotatable part, means to move periodically said driving part into operative position, and means operated by said rotating part upon the completion of a standardizing operation 3 move said driving part out or operative posi- 10. In a self-balancing type of potentiometer having standardizing provisions, the combination of means to operate said standardizing provisions including a driven part. a driving part movable from a first position in which it engages said a driven part to a second position in which it does not engage said driven part, a movable member operative to move said driving part from its secber may move to a position in which it will move said driving part to its first position, means operated by said driven part to move said member to a position in which it will move said driving part to its second position, and means to operate said latch to hold said member in its last mentioned position.

11. In a multiple sell-balancing type potentiometer instrument adapted to make a series of records in sequence of the value oi a plurality of conditions, a detecting member movable from a neutral position to a position on either side thereof, means operated by said detecting member when in its neutral position to make a record of the value of a condition, standardizing mechanism for said potentiometer instrument, means to operate periodically said standardizing mechanism, and means actuated by said means to operate said standardizing mechanism to hold said detecting member out of its neutral position while the standardizing operation is taking place.

12. In a multiple self-balancing potentiometer instrument having a recording mechanism operative to record sequentially the value of a plurality 01 conditions and having a standardizing mechanism operative to recalibrate the instrument, the combination of a detector member movable from a neutral position to a position on either side thereof, means actuated by said detecting member when in its neutral position to operate the recording mechanism to make a rec- 0rd, means to actuate the standardizing mechanism including a rotatable member which rotates ond to its first position and back again, a latch I to hold said member in a position in which it will move said driving part to its second position, periodically operated means and manually operated means to release said latch so said memduring the standardizing operation, and means operated by said rotatable member to move said detecting member out oi its neutral position while a standardizing operation takes place, whereby a recording operation may not occur during that time.

AIDYBIUS I". ALLWEIN,

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